This invention relates to a synchronizing signal generator for circular pattern knitting machines, and more particularly to a signal generator which produces signals exactly synchronized with each of the cylinder needles mounted on a needle cylinder and rotating with the needle cylinder, said signals being applied to needle selector means of electronic circular pattern knitting machines.
Electronic circular pattern knitting machines are capable of knitting articles of various pattern at very high speeds, and have been used as industrial machines for mass production. It is known that circular knitting machines of this type have a needle cylinder having a series of knitting needles arranged at regular intervals for axial sliding movement, and needle selector means which selects cylinder needles according to desired knitting patterns during the high-speed rotation of the needle cylinder and controls the sliding movement of selected needles in axial direction between a knit or operative position for engaging the selected needles with thread and a welt or inoperative position. The known needle selector means includes an electromagnetic actuator which operates to select cylinder needles during the high-speed rotation of the cylinder, and has several different types.
For example, circular knitting machines have a needle cylinder diameter of 760 mm on which a series of about 2,100 needles are mounted and arranged at an extremely small pitch of about 1 mm. A very high-performance needle selector means is therefore required so that the selection of those cylinder needles arranged at such a small pitch and rotating at very high speeds may be carried out within an extremely short period of time and with great accuracy. In a well-known circular knitting machine, cylinder needles are moved at high speeds equivalent to several hundred cycles per second. The needle selector means provided in the circular knitting machine must meet the need of selecting cylinder needles within such very short period of time and with such accuracy, and therefore have limitations to the speed at which the machine should be rotated and its knitting capability. One of the very important factors that influence the property of the needle selector means is the occurrence of irregular reference input signals which are applied to the needle selector means. The needle selector means controls each cylinder needle based on reference input signals which are produced when each needle rotating with the needle cylinder has reached a predetermined position. Those reference input signals must be exactly synchronized with such cylinder needle or needle channel. It is known that suitable sensor means is employed for producing signals which are synchronized with such cylinder needle or needle channel. Photoelectric sensor means such as photo transistor, for example, is known which responds to variations in the light which is transmitted by moving objects. However, the known photoelectric sensor means is very susceptible of dusts from fiber materials when it is employed in circular knitting machines. When it is used in circular knitting machines which particularly require lubrication service, it must have an appreciably lower sensing capability. Other known sensor means include electromagnetic sensor means using electromagnetic elements such as high-frequency coil or element of magnetoresistance. This electromagnetic sensor means is intended for sensing variations in the gap between the sensor and an object. The sensor means is not affected by dusts or lubricated oil, and can be used as suitable means of sensing the movement of cylinder needles or cylinder channels and producing signals which are synchronized with the needles. It contributes largely to decreasing the occurrence of irregular reference input signals which are supplied to the needle selector means. Recently, the need is increasing for a very high speed circular knitting machine, and is followed by a problem as to a drawback that the electromagnetic sensor means has. The drawback is that needle synchronizing signals produced by the electromagnetic sensor contain errors due to the eccentricity or out-of-roundness (hereinafter referred to as "eccentric cylinder") of the needle cylinder. It is known that the needle cylinder comprises so many component parts which are individually machined and assembled. The needle cylinder is inevitably caused to deviate from its center because of the inaccuracy with those parts are machined and assembled. Therefore, the sensor cannot exactly operate due to errors caused by the eccentric needle cylinder. A signal produced by the sensor contains a part that represents any deviation of the cylinder from its center, said part appearing as an irregular part of the reference input signal at the needle selector means, and having a value of magnitude that cannot be disregarded in a high-speed circular knitting machine.
As noted above, the cylinder eccentric content of the signal arises when the needle cylinder deviates from its center, and has a frequency which is clearly lower than the needle synchronizing signal. It may appear that a known high-pass filter may be employed to separate that eccentric content from the needle synchronizing signal. However, in view of the different number of revolutions of the needle cylinder which includes a small number of revolutions ranging from low speed to almost standstill as it is starting or stopping, it will be understood that the use of a high-pass filter is not admittable since the high-pass filter will falsely remove the needle synchronizing signals at such low speeds.